Adding data to (runnning) postgresql with osm2pgsql

Hello,

after following this https://switch2osm.org/manually-building-a-tile-server-18-04-lts/ tutorial I wonder, if it is possible to add additional files to a postgresql, even if it is running.

 osm2pgsql -d gis --create --slim  -G --hstore --tag-transform-script ~/src/openstreetmap-carto/openstreetmap-carto.lua -C 2500 --number-processes 1 -S ~/src/openstreetmap-carto/openstreetmap-carto.style ~/data/azerbaijan-latest.osm.pbf

Will executing this command again, only with a different osm.pbf, result in an error or will it merge the new data into the existing one? What if I add data which the existing data is a subset of (Germany already imported and I execute osm2pgsql with the Europe osm.pbf)? Will it overwrite the existing data?